Sterilization has become an important part of many manufacturing industries. For example, in the pharmaceutical industry, it has become known to pass glass vials and bottles into the path of very hot air by carrying the objects on a moving conveyor belt. These bottles are then subjected to temperatures up to about 350.degree. C. in order to meet the requirements for use in pharmaceutical applications. These standards are perhaps as strict as in any industry where sterilization is employed.
One such device for sterilizing ampules and other pharmaceutical containers is disclosed in Hortig et al, U.S. Pat. No. 3,977,091. Hortig et al teach that laminar flow is needed to reduce contamination by particles which might be otherwise blown about. Laminar flow is achieved by means of distribution plates which cooperate with the air supply means to produce laminar flow downwardly over the objects being treated, such as by heat for sterilization. Hortig et al solve the problem of laminar flow of conditioned air, but that is as far as this prior art patent goes. There is no recognition of any need to provide a complete system to treat the sterilized objects before and after sterilization. The patent does not recognize that some form of heat balance is necessary, particularly when the equipment is used in conjunction with other operations.
Another apparatus for sterilizing containers such as bottles and vials for the pharmaceutical industry is disclosed in Sfondrini et al, U.S. Pat. No. 4,597,192. Sfondrini et al discloses apparatus with a preheat chamber and a coolant chamber on either side of a sterilization chamber. The sterilization chamber itself contains an endless belt which transfers bottles and the like from the wash station onto a discharge for further processing, such as by filling and the like. In Sfrondini et al, pressure is maintained in an outer jacket at a point below the pressure in the sterilization chamber, so that no air will enter the plenum chamber filter system during sterilization step. Air leaves the sterilization environment through a conveyor belt and is drawn upward toward the suction of a fan to return through an outer jacket to the electrical resistance heaters. It is then recycled to the filters, completing a closed air cycle.
One difficulty which is not disclosed in Sfondrini et al but which is a problem arises because the sterilization chamber is operated at a higher pressure than the surrounding environment. The design also relies upon heat from the sterilization chamber to be transferred to the preheat chamber at the inlet of the device. Often times, when such a device is placed adjacent the discharge end of a washing machine, such as a bottle washer, a phenomenon known as blow back occurs. Unless pressure is vented from the preheat zone, 350.degree. C. air can escape back into the washer equipment, melting plastics and other heat sensitive materials and generally damaging or disrupting the washing process.
Another difficulty with prior art devices is that the cooling zone often operates at an even greater pressure than the sterilization zone. Thus, when the pressure becomes excessive in the cooling zone, blow back into the sterilization zone causes a drop in temperature, thereby reducing the effectiveness of the sterilization process. It also causes a greater likelihood of blow back into the preheat zone and ultimately may cause damage to the washer or other equipment preceding the sterilization device itself.
Accordingly, it would be of great benefit to the art if a sterilizing tunnel design could be developed which would be self regulating to bypass excessive pressure and avoid damage to the process and equipment. Specifically, it is an object of the present invention to provide a system which avoids excessive overpressure between stations in the sterilization process. Thus, cool air will no longer infiltrate the sterilization or heating zone sufficiently to reduce the sterilization process. Moreover, the hot air which escapes the hot zone or sterilization zone into the preheat zone will not be permitted to raise the temperature excessively, thereby eliminating blow back into washer equipment and other preprocess equipment.
Other objects will appear hereinafter.